This application is to study excitatory amino acid inputs and calcium- linked neurotransmitter release during opiate withdrawal. The proposed program of research will examine: 1) spontaneous opiate withdrawal in clinical opiate detoxification studies, and 2) naloxone-precipitated opiate withdrawal in a repeated challenge paradigm. The excitatory amino acid contribution to opiate withdrawal will be studied initially with dextromethorphan, a widely used non-opioid antitussive which inhibits excitatory amino acid neurotransmission in pre-clinical studies, and has shown pilot efficacy for treatment of opiate withdrawal. Based on pre- clinical and pilot human studies, the proposed research will determine the anti-withdrawal efficacy of nimodipine, a centrally-acting calcium channel blocker.